Evaluation of the effect of botulinum toxin-a injection into the masseter muscle on salivary flow rate

Aim: The primary objective of this study is to evaluate changes in salivary flow rate before and after treatment in patients with bruxism who received botulinum toxin A injections into the masseter muscle. Secondary objectives include examining the effects of BTX-A injection on pain levels, mandibular function, and patient feedback related to dry mouth. Materials and Methods: In this retrospective clinical study, the data of 44 patients who underwent botulinum toxin A injection into the masseter muscle for the treatment of bruxism between January 1, 2022 and September 1, 2023 at Başkent University Faculty of Dentistry, Oral and Maxillofacial Surgery Outpatient Clinic were included. Saliva samples were collected from each patient in the study group before injection, at 1 week and 1 month after injection by unstimulated saliva collection method and the data were recorded. In addition, relevant questionnaires were administered to the patients to assess the levels of mandibular dysfunction and dry mouth. In order to evaluate the reliability and validity of the unstimulated saliva collection method, an equal number (n=44) of control group was formed and saliva samples recorded from the patients in this group before injection and at 1 week and 1 month after injection were also included in the study. The recorded saliva volume values were subjected to comparative statistical analysis between the study and control groups. Results: Of the 44 patients included in the study, 37 (84.09%) were female and 7 (15.91%) were male. The mean age of the patients was 36.8±13.57 years (18-65 years). There was no significant difference between the study and control groups in terms of gender and age. When the volume values of saliva samples collected before treatment, at week 1 and at month 1 were compared in the study group, the pre-treatment saliva volume value was 1.43±1.31 ml, the saliva volume value at week 1 was 1.71±1.47 ml and the saliva volume value at month 1 was 1.81±1.59 ml. The pretreatment volume value was significantly lower compared to the 1st week and 1st month volume values (p=0.047, p=0.025, respectively). When the volume values of the control group were compared with the volume values of the study group, the volume value of the control group was higher than the pre-treatment volume value of the study group (p=0.045). There was no statistically significant difference between the volume values of the control group and those of the study group at the 1st week and 1st month. According to the results of the mandibular function test; botulinum toxin A injection into the masseter muscle decreased the number of patients who had difficulty in social activities after treatment, while increasing the proportion of patients with normal participation level. In mechanical mastication functions such as biting, chewing and swallowing, the severity of difficulty in handling hard and durable foods generally decreased; the proportion of patients with "no difficulty" or "little difficulty" increased significantly compared to the 'quite' and "very difficult" groups. Functional limitations in daily activities, working and laughing were also alleviated after treatment. According to the results of the dry mouth questionnaire, the responses to the statements "my dry mouth/throat affects the type and amount of food I eat" and "my dry mouth/throat makes me feel uncomfortable" improved statistically significantly. After the treatment, the number of patients who answered "not at all" increased, while the rate of those who answered "somewhat", 'quite' and "definitely" decreased. Conclusion: The study findings revealed that botulinum toxin A injection into the masseter muscle did not lead to a decrease in unstimulated salivary flow rate. However, the increase in salivary flow rate could be attributed to psychosomatic mechanisms in light of the concomitant improvement in mandibular dysfunction scores. Nevertheless, repeated studies in different in vivo experimental models are required to clarify the direct causal dimension of this relationship. This thesis study was approved by Başkent University Medical and Health Sciences Research Board and Ethics Committee (Project no: D-KA 22/15) and supported by Başkent University Research Fund. Keywords: Botulinum Toxin-A, BTX-A, Bruxism, Xerostomy, Unstimulated Salivary Flow Rate